A number of peptide hormones are involved in the control of the different functions in the gastrointestinal (GI) tract, including absorption, secretion, blood flow and motility (Mulvihill, et al. in Basic and Clinical Endocrinology, 4th edition, Greenspan, F. S.; Baxter, J. D., eds., Appleton & Lange: Norwalk, Conn., 1994, pp 551-570). Since interactions between the brain and GI system are critical to the proper modulation of these functions, these peptides can be produced locally in the GI tract or distally in the CNS.
One of these peptide hormones, motilin, a linear 22-amino acid peptide, plays a critical regulatory role in the GI physiological system though governing of fasting gastrointestinal motor activity. As such, the peptide is periodically released from the duodenal mucosa during fasting in mammals, including humans. More precisely, motilin exerts a powerful effect on gastric motility through the contraction of gastrointestinal smooth muscle to stimulate gastric emptying, decrease intestinal transit time and initiate phase III of the migrating motor complex in the small bowel (Itoh, 1, Ed., Motilin, Academic Press: San Diego, Calif., 1990, ASIN: 0123757304; Nelson, D. K. Dig. Dis. Sci. 1996, 41, 2006-2015; Peeters, T. L.; Vantrappen, G.; Janssens, J. Gastroenterology 1980, 79, 716-719).
Motilin exerts these effects through receptors located predominantly on the human antrum and proximal duodenum, although its receptors are found in other regions of the GI tract as well (Peeters, T. L.; Bormans, V.; Vantrappen, G. Regul. Pept. 1988, 23, 171-182). Therefore, motilin hormone is involved in motility of both the upper and lower parts of the GI system (Williams et al. Am. J. Physiol. 1992, 262, G50-G55). In addition, motilin and its receptors have been found in the CNS and periphery, suggesting a physiological role in the nervous system that has not yet been definitively elucidated (Depoortere, I.; Peeters, T. L. Am. J. Physiol. 1997, 272, G994-999 and O'Donohue, T. L et al. Peptides 1981, 2, 467-477). For example, motilin receptors in the brain have been suggested to play a regulatory role in a number of CNS functions, including feeding and drinking behavior, micturition reflex, central and brain stem neuronal modulation and pituitary hormone secretion (Itoh, Z. Motilin and Clinical Applications. Peptides 1997, 18, 593-608; Asakawa, A.; Inui, A.; Momose, K.; et al., M. Peptides 1998, 19, 987-990 and Rosenfeld, D. J.; Garthwaite, T. L. Physiol. Behav. 1987, 39, 753-756). Physiological studies have provided confirmatory evidence that motilin can indeed have an effect on feeding behavior (Rosenfeld, D. J.; Garthwaite, T. L. Phys. Behav. 1987, 39, 735-736).
The recent identification and cloning of the human motilin receptor (WO 99/64436) has simplified and accelerated the search for agents which can modulate its activity for specific therapeutic purposes.
Due to the critical and direct involvement of motilin in control of gastric motility, agents that either diminish (hypomotility) or enhance (hypermotility) the activity at the motilin receptor, are a particularly attractive area for further investigation in the search for new effective pharmaceuticals towards these indications.
Peptidic agonists of the motilin receptor, which have clinical application for the treatment of hypomotility disorders, have been reported (U.S. Pat. Nos. 5,695,952; 5,721,353; 6,018,037; 6,380,158; 6,420,521, U.S. Appl. 2001/0041791, WO 98/42840; WO 01/00830 and WO 02/059141). Derivatives of erythromycin, commonly referred to as motilides, have also been reported as agonists of the motilin receptor (U.S. Pat. Nos. 4,920,102; 5,008,249; 5,175,150; 5,418,224; 5,470,961; 5,523,401, 5,554,605; 5,658,888; 5,854,407; 5,912,235; 6,100,239; 6,165,985; 6,403,775).
Antagonists of the motilin receptor are potentially extremely useful as therapeutic treatments for diseases associated with hypermotility and hypermotilinemia, including irritable bowel syndrome, dyspepsia, gastroesophogeal reflux disorders, Crohn's disease, ulcerative colitis, pancreatitis, infantile hypertrophic pyloric stenosis, diabetes mellitus, obesity, malabsorption syndrome, carcinoid syndrome, diarrhea, atrophic colitis or gastritis, gastrointestinal dumping syndrome, postgastroenterectomy syndrome, gastric stasis and eating disorders leading to obesity.
A variety of peptidic compounds have been described as antagonists of the motilin receptor (Depoortere, I.; Macielag, M. J.; Galdes, A.; Peeters, T. L. Eur. J. Pharmacol. 1995, 286, 241-247; U.S. Pat. Nos. 5,470,830; 6,255,285; 6,586,630; 6,720,433; U.S. 2003/0176643; WO 02/64623). These peptidic antagonists suffer from the known limitations of peptides as drug molecules, in particular poor oral bioavailability and degradative metabolism.
Cyclization of peptidic derivatives is a method employed to improve the properties of a linear peptide both with respect to metabolic stability and conformational freedom.
Cyclic molecules tend to be more resistant to metabolic enzymes. Such cyclic tetrapeptide motilin antagonists have been reported (Haramura, M. et al J. Med. Chem. 2002, 45, 670-675, U.S. 2003/0191053; WO 02/16404).
Other motilin antagonists, which are non-peptidic and non-cyclic in nature have also been reported (U.S. Pat. Nos. 5,972,939; 6,384,031; 6,392,040; 6,423,714; 6,511,980; 6,624,165; 6,667,309; U.S. 2002/0111484; 2001/041701; 2002/0103238; 2001/0056106, 2002/0013352; 2003/0203906 and 2002/0002192)
The macrocyclic motilin antagonists of the present invention comprise elements of both peptidic and non-peptidic structures in a combination which has not been pursued for this application previously.
Indeed, the structural features of antagonists of the present invention are different. In particular, within the known motilin antagonists which are cyclic peptides, it was found that such derivatives containing D-amino acids were devoid of activity. In contrast, for the tripeptidomimetic compounds of the present invention, the D-stereochemistry is required for two of the three building elements.
The motilin antagonists of the present invention are also distinct from the prior art in that they comprise a tether element to fulfill the dual role of controlling conformations and providing additional sites for interaction either through hydrophobic interactions, hydrogen bonding or dipole-dipole interactions.